An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A measure of the blurring and degradation of the image of astronomical objects caused by → turbulence in the Earth's atmosphere, including the telescope environment. Seeing causes the images of stars to break up into → speckle patterns, which change very rapidly with time. See also → Fried parameter; → differential image motion monitor.

→ see; → -ing.

Šekân "wrinkle, plait; curl; rupture, breach," variant of šekan "fold, curl; ripples on water," from šekastan "to break, split;" Mid.Pers. škastan "to break;" Av. scind-, scand "to break, cleave;" Proto-Iranian *skand- "to break, cleave;" PIE sken- "to cut off."

The angular size of a stellar image for long exposures, as determined by the ratio λ/r₀, where λ is the wavelength and r₀ the typical size of → turbulence patches. → Fried parameter. The most common seeing measurement is the → full-width at half-maximumof the seeing disk. → Airy disk.

→ seeing; → disk.

An optical instrument that follows the variation of → atmospheric turbulence by continuously measuring the → seeing conditions.

→ seeing; → monitor.

1) Of a line, that portion bounded by two points.
2) Of a circle, that portion of a plane bounded by an arc of the circle and its chord.
3) Of a sphere, the solid formed between two parallel planes that cut through a sphere.
4) In computer science, a portion of a program, often one that can be loaded and executed independently of other portions.

From L. segmentum "a strip or piece cut off," originally a geometric term, from secare "to cut" + -mentum "-ment."

Borank, from Kermâni borang "a slice (of fruit);" Borujerdi boleng "piece, section," ultimately from *brin-ka- (probable contracted forms Lari peng and pengi "portion or part of anything"), related to boridan "to cut off;" Mid.Pers. brīn-, blyn-, britan, brinitan "to cut off," Av. brī- "to shave, shear," brin- (with prefix pairi-); cf. Skt. bhrī- "to hurt, injure," bhrinanti "they hurt;" PIE base bhrei- "to cut, pierce."

A large telescope mirror consisting of smaller mirror segments designed to act as a single, larger reflecting surface. Because current monolithic mirrors cannot be constructed larger than about eight meters in diameter, the use of segmented mirrors is a key component for larger aperture telescopes.

Segmented, p.p. of → segment (v.); → mirror.

To separate or set apart from others or from the main body or group; isolate.

From M.E. segregat, from L. segregatus, p.p. of segregare "separate from the flock, isolate, divide," from se- "apart from" + greg-, ablative of grex, gregis "herd, flock, crowd," cf. Gk. gergera "swarm, flock;" maybe related to Old Khotanese -gris- in hamgris- "to assemble."

Savâyidan, from savâ "separate, apart;" probably related to Mid.Pers. s'w- "to crush," sây- "to rub, wear, tear;" cf. Kurd. (Hawramân) sawa, Roshani sêw-/sêwt, Bartangi siw-/siwd, Yazghulani saw-/sed, Bajui sâw-/sâwd "to rub, smear, grind" (Cheung 2007); Mod.Pers. sây-/sudan "to rub, wear, tear, grind, dissolve;" cf. Skt. śā- "to sharpen, whet."

The act or practice of segregating. The state or condition of being segregated. → mass segregation.

Verbal noun of → segregate.

Of, subject to, or caused by → vibrations of the → Earth. → seismic wave.

From seism, → seismo-, + → -ic.

An → elastic wave generated in the → Earth by an → impulse such as an → earthquake or an → explosion. Seismic waves may travel either along or near the Earth's surface or through the Earth's interior.

→ seismic; → wave.

A combining form meaning "earthquake;" → seismology, → seismograph, etc.

From Gk. seismo- combining form of seismos "shock, earthquake," from seiein "to shake."

Larzé-, from larzé "shaking, trembling," from larzidan "to tremble, shiver;" Mid.Pers. larzidan "to shake, tremble;" Manichean Mid.Pers. rarz- "to shiver with fever;" Proto-Iranian *rarz- "to shake, tremble."

An instrument that detects, magnifies, and records → seismic waves, especially those caused by → earthquakes or → explosions.

→ seismo-; → -graph.

The branch of geophysics that is concerned with the study of earthquakes and measurement of the mechanical properties of the Earth.

→ seismo-; → -logy.

Not → often; rarely.

M.E., from O.E. seldum, variant of seldan; cognate with Ger. selten, Goth. silda-, Dutch zelden.

Adverb from perz, → rare.

To choose from among several.

From L. selectus, p.p. of seligere "to choose out, gather apart," from se- "apart" + legere "to gather, select."

Gozidan "to select, choose;" Mid.Pers. vicitan, wizidan, wizin- "to choose, select, discriminate," related to cin-, cidan "to gather, collect;" Av. vicidāi- "to discern," viciθa- "separation, discernment;" from vi- "apart, away from" (O.Pers. viy- "apart, away;" cf. Skt. vi- "apart, asunder, away, out;" L. vitare "to avoid, turn aside") + kay- "to choose;" cf. Skt. ci- "to gather, heap up," cinoti "gathers."

Any of a set of rules specifying the relationships between the → quantum numbers that characterize the initial and final states of a quantum-mechanical system in a → discrete transition. Transitions that do not agree with the selection rules are called → forbidden and have considerably lower probability. There are several types of selection rules (→ rigorous selection rule, → LS coupling, etc.) for → electric dipole transition (→ permitted), → magnetic dipole (forbidden), electric → quadrupole (forbidden), etc.

Selection, verbal noun of → select; → rule.

Absorption which varies with the wavelength of radiation incident upon an absorbing substance.

Selective, verbal noun of → select; → absorption.

A type of scattering that occurs when certain → particles are more effective at scattering a particular → wavelength of light, as in → Rayleigh scattering.

→ selective; → scattering.

Same as → horizontal eclipse.

From Gk. selene "Moon," related to sela "light, brightness, flame," + helion, → sun.

→ horizontal eclipse.

Same as → horizontal eclipse.

From Fr. selenelion, contraction of → selenehelion.

→ horizontal eclipse.

Referring to or pertaining to the center of the Moon.

Formed on the model of → geocentric, from seleno- combining form of Gk. selene "moon" + -centric, from → center + → -ic.

Mâh-markazi, from mâh, → moon, + markazi, from markaz, → center, + -i, → -ic.